1. Field of the Invention
The present invention relates to a method of deposition. More particularly, the present invention relates to a method for forming a contact plug.
2. Description of the Related Art
In general, contact resistance is dependent upon the contact area or dimensions of the contact window. As dimensions of the contact window shrink, contact resistance will increase correspondingly. For a device having a line width smaller than 0.18 .mu.m, contact resistance can be so high that special processing steps have to be executed.
In the design of DRAMs, a polysilicon plug is one of the most common contact structures for connecting a conductive layer with an N+ or an N- silicon substrate. The contact is a polysilicon/polysilicon contact region. One of the problems for forming such a contact structure is that a layer of thin native oxide is usually formed at the substrate surface due to exposure to air during processing. Although the thin native oxide layer has little effect on contact resistance when the contact area is large, the presence of a native oxide layer can increase contact resistance considerably when the contact opening is small.